1. Field of the Invention
The present invention relates to an automatic document feeder to be applied to an image processing apparatus such as a copying machine, a facsimile machine or an image reader.
2. Description of Related Art
Automatic document feeders are conventionally known which are applied to copying machines and the like and adapted to separate document originals set on a document placing plate on a one-by-one basis and feed the separated document original to a copying position through a document transportation path. The separation of the document originals is typically achieved by cooperation of a separator roller and a separator belt.
The positional relation between the separator roller and the separator belt is important in order to assuredly prevent plural document feeding and separate the lowermost document original from the other document originals. Therefore, it is basically preferred that the separator roller and the separator belt are fixed in place to maintain a predetermined positional relation. However, paper jam in a sheet transportation system is unavoidable, and the fixing of the separator roller and the separator belt makes it difficult to perform a jam recovery operation.
In order to facilitate the jam recovery operation with a separator roller and a separator belt maintained in a predetermined positional relation, a conventional document feeder is constructed such that a cover openable with respect to a main body is attached to the main body and the separator belt is slightly brought apart from the separator roller when the cover is opened.
More specifically, the separator belt is attached to the main body with its one axial side fixed to the main body and with its other axial side being vertically movable pivotally about the one axial side and, when the cover is closed, a pressure is applied to the other axial side of the separator belt. Therefore, when the cover is opened, the pressure applied to the separator belt is relieved so that the other axial side of the separator belt can be brought apart from the separator roller. Since the one axial side of the separator belt is fixed, the positioning of the separator belt with respect to the separator roller can be controlled to a certain extent when the cover is closed.
With this construction, since the separator belt cannot fully be brought apart from the separator roller but only the one axial side thereof can be brought apart from the separator roller, the separator belt hinders the removal of a jammed document original. Therefore, the jam recovery operation cannot readily be performed.
In order to assuredly separate a document original, a separator belt should be positioned with respect to a separator roller in an overlapped relation with a predetermined overlap amount. The overlap amount corresponds to a distance between a top portion of the separator roller and an under face of the separator belt.
In the aforesaid conventional document feeder, the proper positioning of the separator belt with respect to the separator roller is not maintained when the cover is opened. Therefore, when the cover is closed after the jam recovery operation, the separator belt should accurately be positioned with respect to the separator roller. To this end, the conventional document feeder employs an overlap defining member for defining the overlap amount. The overlap defining member permits the separator belt to be positioned with respect to the separator roller with the predetermined overlap amount when the cover is closed.
However, users may use document originals having different thicknesses. Therefore, fixing the overlap amount may result in document feeding failures such as plural document feeding.
In the prior art, if the overlap amount is not suitable for a document thickness, an overlap defining member providing a proper overlap amount for this particular document thickness should be employed. This entails a troublesome operation for replacement of the overlap defining member.